I don't think that this is a feature -- for how would it know whether a field is being used or not?

Just because a field is not present in any view doesn't mean its not being used. I use fields all the time that are never present in any view.

The best solution is to clean up as you go. If you stop using a field and you know you won't use it any more -- remove it then. Don't wait until your done with the template.